title: Permeability of the cell-to-cell membrane channel and its regulation in an insect cell junction.
abstract: Cells of organs and tissues commonly communicate directly with one another via permeable membrane junctions. Cell-to-cell channels, spanning the width of both membranes of a junction, are thought to provide the pathways between the cytoplasms of adjacent cells for the immediate exchange of ions and small molecules. We study these cell-to-cell channels in a cell model system, the salivary gland of Chironomus. Using intracellularly injected fluorescent labelled peptides and oligosaccharides of various molecular dimensions as channel permeability probes we find the channels to have a bore of about 2 nm. The channel permeability can be modulated and, in the extreme, the channels can be closed under various experimental conditions. With the aid of the Ca2+-sensitive photoprotein aequorin as monitor of cytoplasmic free Ca2+ concentration, we show that a determining factor in this modulation of channel permeability is the cytoplasmic free Ca2+ concentration. Moreover, results obtained by injection of different-sized and different-labelled channel permeability probes together with Ca2+ indicate that closure of the individual channels may occur in more than one step, i.e., by a graded reduction of channel bore.
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism; D002450:Cell Communication; D002463:Cell Membrane Permeability; D002683:Chironomidae / Q000378:metabolism; D003619:Dansyl Compounds; D016650:Fluorescein-5-isothiocyanate; D005452:Fluoresceins; D007365:Intercellular Junctions / Q000378:metabolism* / Q000648:ultrastructure; D012235:Rhodamines; D012469:Salivary Glands / Q000378:metabolism; D013861:Thiocyanates
chemical_list: D003619:Dansyl Compounds; D005452:Fluoresceins; D012235:Rhodamines; D013861:Thiocyanates; C022027:lissamine rhodamine B; D016650:Fluorescein-5-isothiocyanate; D002118:Calcium